The present invention relates in general to controlled fluid delivery systems. More particularly, the invention relates to an improved paint spray gun device.
Hand-held spray devices are used in a variety of utility applications for the delivery of material, such as fine solid particulate material, and fluid or liquid substances, such as paints, liquid chemicals and the like that are capable of being atomized and directed through a spray emission control nozzle onto a given target area. Spray guns used in spray painting systems atomize the liquid paint by means of atomizing air which enters the nozzle area via a chamber which surrounds a fluid nozzle. The paint is atomized by the accelerating burst of this air as it exits the nozzle via a central aperture located at the end of the chamber. The initial conventional pattern of the atomized liquid and air mixture is in cross section a circle as long as the exit aperture is circular.
When the compressed air source for a spray painting apparatus utilizes a high volume, low pressure compressor, it is conventional for the exit nozzle on the spray painting gun to have a central aperture which is considerably larger than the circumscribed liquid nozzle. The large amount of air utilized in a conventional spray paint nozzle is due to the relative size of the central aperture compared to that of the liquid nozzle.
It is now known that the spray pattern of a paint spray gun can be adjusted via the use of an adjustment screw for the needle. One known such design is illustrated in U.S. Pat. No. 4,915,303 which is owned by the assignee of the instant application. That patent is incorporated herein by reference in its entirety.
Such a device customarily comprises a hand-held spray gun unit having a pistol grip or handle and a barrel. An operator uses the handle both to hold the spray gun and to operate a trigger mechanism for controlling the emission of a fluid, such as paint, from a nozzle element positioned in the barrel. The spray pattern delivered by the nozzle element is controlled by a rotatable wheel mounted at the rear of the spray gun unit. Located beneath the nozzle element is a storage container attachment fitting through which a storage container or tank, usually in the form of a bottle, is mounted on the spray gun. The tank is usually pressurized and its contents are drawn into an internal delivery line within the spray gun unit and ported to the nozzle element. To pressurize the contents of the storage container, its top or lid is fitted with a pressure port to which a fluid line is attached in order to establish a prescribed "head" pressure above the material held in the container. Mounted on the gun is a pressure regulator valve having an inlet port which is coupled to the air inlet line and an outlet port which is coupled to the main pressure inlet port in the barrel of the gun. This valve allows the operator to set the spray nozzle emission control pressure. For a typical industrial paint spraying application, such as in an automobile body repair facility, the nozzle pressure may be on the order of anywhere from 25 to 100 psi. In contrast, the head pressure in the storage container is considerably lower than the main supply pressure and may be on the order of 5 to 10 psi.
On a conventional high volume, low pressure conversion gun, i.e. a gun which uses a high pressure air supply (from 10 to 125 psig) but sprays fluid at a low pressure (i.e. under 10 psig), closing the fan aperture in the gun increases the atomizing pressure or "head" pressure in the paint container dramatically if the inlet pressure is not reduced. For pressure feed systems, this can be a problem because the fluid container cups can be overpressurized. Conceivably, the bottom of the container cup can be blown out. Such a pressure increase or pressure spike is also disadvantageous from the standpoint that the coating compositions sprayed by the gun will not flow evenly. There also may be too much air mixed in with the coating composition which is to be sprayed, resulting in difficulties in the spraying process.
Another patent which discloses a conventional paint spray nozzle is U.S. Pat. No. 4,948,053 which is assigned to the assignee of the instant application. That patent is also incorporated herein by reference in its entirety.
Accordingly, it has been considered desirable to develop a new and improved fluid spray gun which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.